diff --git a/sql/mysql_priv.h b/sql/mysql_priv.h
index c60fc1937f7..1ab8936df4c 100644
--- a/sql/mysql_priv.h
+++ b/sql/mysql_priv.h
@@ -872,7 +872,7 @@ public:
   Lazy_string_str(const char *str_arg, size_t len_arg)
     : Lazy_string(), str(str_arg), len(len_arg) {}
   void copy_to(String *dst) const
-  { dst->copy(str, len, system_charset_info); }
+  { dst->copy(str, (uint32)len, system_charset_info); }
 };
 
 class Lazy_string_num : public Lazy_string